A magnetic random access memory (MRAM; hereinafter, simply referred to as “MRAM device”) device uses a magnetic tunnel junction (MTJ) including a metal stacked film in which an insulating layer is interposed between two layers of magnetic materials. The MRAM device is formed of a multilayered film including a metal stacked film containing cobalt (Co) or the like.
A metal stacked film has the boiling point of higher than about 1000° C. Thus, conventionally, a metal stacked film has mainly been etched by sputtering. Recently, there has been suggested a method of dry etching a metal stacked film of a MRAM device. By way of example, in Patent Document 1, there has been suggested a method of dry etching a metal stacked film of a MRAM device by using an etching gas containing a chlorine gas (Cl2) or a fluorine gas (F2).
Patent Document 1: Japanese Patent Laid-open Publication No. 2002-230720
However, if a metal stacked film is dry etched by using an etching gas containing a chlorine gas (Cl2) or a fluorine gas (F2), a reaction product containing chlorine (Cl) or fluorine (F) is generated during the etching process. The reaction product containing chlorine (Cl) or fluorine (F) is difficult to be evaporated and remains within a processing chamber. As a result, the reaction product is deposited on a wall surface of the metal stacked film by etching, so that a shape of a base layer is damaged. Further, since the reaction product containing chlorine (Cl) or fluorine (F) is difficult to be evaporated, it is also difficult to remove the reaction product from the etched surface, and, thus, a target line width (CD: Critical Dimension) cannot be obtained, which makes it difficult to control the etching process.
By way of example, if a metal stacked film contains cobalt (Co), when the metal stacked film is dry etched by using an etching gas containing a chlorine gas (Cl2) or a fluorine gas (F2), a reaction product generated during the etching process contains a reaction product generated from a reaction between cobalt (Co) and chlorine (Cl) or a reaction product generated from a reaction between cobalt (Co) and fluorine (F). Herein, a compound of cobalt (Co) and chlorine (Cl) has the melting point of 737° C., and a compound of cobalt (Co) and fluorine (F) has the melting point of 1127° C. If a compound has a high melting point as such, a reaction product generated during an etching process is difficult to be evaporated and remains within a processing chamber. In order to perform an etching process with high efficiency and to obtain a vertical etching profile, it is important to select an etching gas from which a reaction product having low melting point and boiling point is generated such that the reaction product can be immediately evaporated and exhausted during the etching process.